Optical information recording media represented by optical disks have the following merits as compared to the magnetic information recording media: (1) Recording density is high; (2) Reproduction can be conducted with no contact with the media, with the resultant decreased likelihood of the influence of scratches or dusts; (3) Serious damage does not occur even if they are touched by hand, resulting in easy handling; (4) Readout pick-up only undergoes less consumption; (5) Various reproduction modes are available, and the like, and they have made rapid progress in recent years. For information recorded, there are a wide variety of data used for music, images and/or computers.
In the case of manufacturing recording media only for reproduction, e.g., optical disks, etc., there are employed an injection method or a compression method. In these methods, a metal mold is provided. The metal mold is an original block on which information to be recorded is recorded as an uneven or irregular pattern. In the injection method, resin, e.g., polymethyl methacrylate (PMMA), or polycarbonate (PC), etc. is injected into the metal mold, and in the compression method, resin is compressed to the metal mold. Thus, by repeating resin injection or compression using a metal mold serving as an original block, a great deal of replicas are manufactured.
The conventional prior art as stated above have the following problems.
(1) Since conventional optical disks have a thick, rigid medium, they have a large capacity and take up a broad space, so that they are inconvenient to carry. In addition, broad exhibition space is required at the time of selling.
(2) With the conventional methods of manufacturing optical disks, it is difficult to carry out mass production. As previously described, it is required for the injection method to inject thermoplastic resin into the metal mold vessel under a pressurized condition. On the other hand, with the compression method, it is required to mold-press thermoplastic resin into the metal mold while heating it, and thereafter to remove the resin from the metal mold after the resin is cooled until its temperature is below the thermal deformation temperature. Accordingly, it takes considerable time for replicating one optical disk.
(3) Since a metal mold is exposed to high temperatures in the conventional manufacturing methods for an optical disk, if it is repeatedly used for a long time, its surface is oxidized and thus and uneven pattern is deformed, resulting in lowered reproducibility of information to be recorded.